1. Force and Motion 2011

2. First we need to define the word FORCE:
A push or pull resulting from the interaction of two objects.
Two types of forces
Pushes
Pulls

3. Describing Forces Forces can be described by…
The size of the force, known as magnitude
The direction of the force
Both factors can be represented by an arrow, known as a VECTOR.

4. Measuring Forces Forces are measured in Newtons SI unit of force
Symbol: N
Measured by using a spring scale

5. Forces may be balanced or unbalanced
Balanced forces – all forces acting on an object are equal
There is NO MOTION
Unbalanced forces – one or more forces acting on an object are stronger than others
There is MOTION
Net Force is the combination or total of all forces acting on an object

6. Calculating Net Force
Net Force = 2 N right
Net Force = 10 N right
When forces act in the SAME DIRECTION, you must ADD the forces to determine the net force.
When forces act in OPPOSITE DIRECTIONS, you must SUBTRACT the forces to determine the net force.

7. Newton’s Laws and Forces
First Law – Inertia, Unbalanced/Balanced, Friction
Second Law – Acceleration, Force & Mass
Third Law – Action-Reaction

8. What is Friction? Friction force that opposes the motion of an object
the force of friction works in the opposite direction of the force of motion
Friction slows things down

9. Types of Friction Sliding Kinetic Friction Rolling Kinetic Friction
the source of friction is the contact between two surfaces, at least one of which is in motion
Rolling Kinetic Friction
friction between two surfaces that are not in constant contact
ex. Wheels
Static Friction
When a force is applied to an object but that force does not cause the object to move
Air Resistance
friction results from air pushing on an object as it is moving

10. Harmful vs. Helpful Friction
Friction can be both harmful and helpful to us in our everyday lives.
HARMFUL FRICTION
HELPFUL FRICTION
Holes in your socks or jeans
Paper and pencil to write
Erosion of topsoil
Walking without slipping
Worn/rusted car parts
Brakes on a car
Sliding on a banana peel
Moving furniture

11. Ways to Reduce/Increase Friction
Use of Lubricants such as oil, wax, or grease
Make surfaces smoother
Switch from sliding to rolling kinetic friction
Increase the amount of force being applied

12. What is motion?
When an object’s distance changes relative to a reference point.

13. What is a reference point?
An object used for comparison to see if something is in motion!

14. So….How do you know that you are moving?
It depends on how you look at things.
You can use different reference points to justify the motion of the same object.
Look at the books on your table. Are they moving? Use the floor as a reference point.
What if the sun is your
reference point?

15. More examples…. Explain how the illustrations are examples of motion and no motion.

16. Speed
The distance traveled divided by the time taken to travel that distance
Speed = Distance ÷ Time

17. Units for Speed….
Units for speed will be unit of distance over a unit of time
(miles per hour or meters per second)
Units for distance are
(millimeters, centimeters, kilometers etc.)
Units for time will be
(seconds, minutes, hours etc.)

18. SPEED IN A GIVEN DIRECTION!
WHAT IS VELOCITY?
SPEED IN A GIVEN DIRECTION!
Example:
The Atlanta Falcons are traveling to Miami to play the Dolphins. The team bus travels at 90km/hr. What is the velocity of the bus?

19. WHAT IS ACCELERATION?
When an object does ANY of the following, it is called acceleration…
Speeds up
Slows Down (deceleration)
Changes Direction
Calculating Acceleration
(Final Velocity – Original Velocity )÷ Time

20. What is Gravity?
Gravity is force of attraction between all objects in the universe

21. Law of Universal Gravitation
All objects in the universe attract each other through gravitational force.
The size of the force depends on an objects
Mass
Distance between the objects

22. Gravity is affected by distance
the greater the distance between two objects, the smaller the gravitational force
Increased force of gravity
Decreased force of gravity

23. Gravity is affected by mass
the larger an object’s mass, the greater the gravitational force
Not much gravity
More gravity
Lots of gravity

24. Air Resistance
Air resistance is the force that opposes the motion of objects through air.
The amount of air resistance acting on an object depends on:
The size of the object
The shape of the object
The speed of the object